It is possible to replace the grinding material on the hub of a grinding wheel, particularly to re-electroplate a CBN wheel around the hub and the cost of such a refurbishment of an existing hub is far less than the cost of replacing the wheel in its entirety. However if all of the grinding material is stripped away from any part of the hub during the grinding process, the hub cannot normally be refurbished in this way, and in particular cannot be replated with CBN material. In this event, the wheel has to be scrapped. It should therefore be of financial benefit to an end user of grinding wheels, particularly Electroplated CBN wheels, to be able to predict the point in time just prior to when the grinding material is liable to be stripped from the hub and to allow the machine to be stopped before the wheel is irreparably damaged.
Previously it has been thought that the most suitable method for monitoring a grinding wheel was via the increased in grind power which arises as the wheel wears. Past tests have shown that the increase in grind power over the life of the wheel to be about 50% but most of this increase is found to occur during the machining of the last half to 1% of the normal life expectancy of the wheel. Thus if the normal life of a wheel is expressed in terms of the number of similar workpieces which can be ground by the wheel before it is worn down to the hub, and the normal life is say 4,000 workpieces, then the 50% increase in grind power is only found to occur during the last 20 or 30 workpieces.
This pattern is typical for a grinding wheel performing cylindrical grinding in which the grinding face of the wheel is plain, i.e. the grinding process is substantially uniform over the width of the wheel.
For many grinding processes, the face of the wheel is not plain, but is required to include at least one and sometimes two or three peripheral ridges which it is found tend to wear away more quickly than the remaining surface of the wheel. This is particularly common when grinding sidewalls with undercuts. Each of the rims of the grinding wheel have to remove considerably more metal than the central region of the wheel and the power increase pattern for such a wheel when performing this type of grinding is rather different and there is only a minimal increase in power before the grinding material is completely stripped from the wheel due to the wheel wear occurring disproportionally over the width of the wheel.
It is an object of the present invention to provide an alternative method of monitoring a grinding wheel's performance which provide a reliable warning of when the grinding material, particularly Electroplate CBN material, is found to wear away, even when the wear is excessive and uneven over the width of the wheel.